Problem: Ishaan did 12 more push-ups than Tiffany at night. Tiffany did 18 push-ups. How many push-ups did Ishaan do?
Answer: Tiffany did 18 push-ups, and Ishaan did 12 more than that, so find the sum. The sum is $18 + 12$ push-ups. He did $18 + 12 = 30$ push-ups.